linux-kernel - Re: [PATCH 1/2] lib: hexdump: use a look-up table to do hex_to

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Message-ID: <1467314771.24287.160.camel@perches.com>
Date:	Thu, 30 Jun 2016 12:26:11 -0700
From:	Joe Perches <joe@...ches.com>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Michal Nazarewicz <mina86@...a86.com>, zengzhaoxiu@....com,
	linux-kernel@...r.kernel.org
Cc:	Zhaoxiu Zeng <zhaoxiu.zeng@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	Borislav Petkov <bp@...e.de>, Michal Hocko <mhocko@...e.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Nicolas Iooss <nicolas.iooss_linux@....org>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Horacio Mijail Anton Quiles <hmijail@...il.com>
Subject: Re: [PATCH 1/2] lib: hexdump: use a look-up table to do hex_to_bin

On Wed, 2016-06-29 at 21:52 +0300, Andy Shevchenko wrote:
> On Wed, 2016-06-29 at 20:31 +0200, Michal Nazarewicz wrote:
[]
> > tolower macro maps to __tolower function which calls isupper to
> > to determine if character is an upper case letter before converting
> > it to lower case.  This preservers non-letters unchanged which is
> > what you want in usual case.
> > 
> > However, hex_to_bin does not care about non-letter characters so
> > such conversion can be performed as long as (i) upper case letters
> > become lower case, (ii) lower case letters are unchanged and (iii)
> > non-letters stay non-letters.
> > 
> > This is exactly what _tolower function does and using it makes it
> > possible to avoid _ctype table lookup performed by the isupper
> > table.
> > 
> > Furthermore, since _tolower conversion is done unconditionally, this
> > also eliminates a single branch.
> This change I agree with since _tolower() is specific for lib internal
> usage in the kernel.

Perhaps _tolower should be used a bit more in lib
---
 lib/string.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/string.c b/lib/string.c
index ed83562..b0e72fd 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -53,8 +53,8 @@ int strncasecmp(const char *s1, const char *s2, size_t len)
 			break;
 		if (c1 == c2)
 			continue;
-		c1 = tolower(c1);
-		c2 = tolower(c2);
+		c1 = _tolower(c1);
+		c2 = _tolower(c2);
 		if (c1 != c2)
 			break;
 	} while (--len);
@@ -69,8 +69,8 @@ int strcasecmp(const char *s1, const char *s2)
 	int c1, c2;
 
 	do {
-		c1 = tolower(*s1++);
-		c2 = tolower(*s2++);
+		c1 = _tolower(*s1++);
+		c2 = _tolower(*s2++);
 	} while (c1 == c2 && c1 != 0);
 	return c1 - c2;
 }